Wicks for Self-Watering Pots

First, work out which pot you have

This is a thirty-second check and it decides everything that follows. Lift the plant out, or look down the fill tube.

If you can see a rope, a felt strip or a fabric tail reaching down into a water chamber, you have a wicking pot. The wick is the only transport path there is, and when it fails the pot stops working while still looking full.

If the mix itself sits on or dips into the water - a granulate layer, a slotted false floor, a column of soil reaching down - you have a sub-irrigated reservoir pot. Capillary rise happens through the growing medium. Adding a rope to one of these changes nothing useful.

Some designs use both: a granulate layer with a wick to start the column. Our comparison of the two mechanisms goes through how each one fails and how you would know. This page is about what to buy once you know you need a wick.

The specification nobody publishes

Everywhere else on this site the number that decides a recommendation is reservoir capacity, or a delivery rate in milliliters per day. The Blumat stakes publish about 75 ml per day. GrowOya publishes capacity for every size it sells.

Not one wicking cord on the market publishes a delivery rate. Not one publishes a service life either. What you get is a diameter and a length, which is two facts short of being able to compute anything.

That absence is why the mixed-diameter set is ranked first. It is not a better cord than the single-diameter spools - it is the same cotton rope. It is ranked first because when the maker will not tell you the rate, the only way to find the right diameter for your pot and your mix is to fit one, watch it for a week, and change it if the mix is too wet or too dry. Five diameters in one cheap pack is that experiment.

How we judged these

Diameter range offered. A wick that is too thick keeps a small pot permanently saturated, which is the condition that causes root rot in reservoir pots. Too thin and an 8-inch pot dries out. Diameter is the only variable you control, so being able to choose it matters more than anything else here.

Length per dollar. A wick is a consumable. It mineralizes, and in hard water it mineralizes faster. Buying enough cord that replacing one is a two-minute job rather than another order is the practical difference between a working setup and an abandoned one.

Material behavior in hard water. Cotton is the default and it works, but it rots eventually and stiffens as calcium deposits build in the fibers. Nylon does not rot. Nothing in this category publishes a service life for either, so this is judged on material properties rather than on a maker’s figure.

Whether a wick is the right tool at all. Two of the five picks here are not cord, because for a tray of small pots a felt mat is a better answer, and for someone who would rather not assemble anything a pot with the wick already fitted is the honest recommendation.

Which diameter for which pot

With no published rates, the only sound basis for this is the volume of water the pot actually needs, which this site does compute. One thorough watering is about 100 ml for a 4-inch pot, 350 ml for a 6-inch, and 800 ml for an 8-inch - the full derivation is on the methodology page.

A thicker wick moves more water per day. So the sizing logic is simply that the water demand rises steeply with pot diameter - an 8-inch pot wants eight times what a 4-inch pot does - and the wick has to keep up without overshooting.

The last row is the honest one. A wick has a limited delivery rate, and a large plant in a 10-inch pot will outrun it in summer. For a floor plant the answer is capillary rise through the medium itself, which is what a large reservoir planter does, not a rope.

How to fit one

Four steps, and the third is the one people get wrong.

1. Soak the cord first. A dry wick does not start wicking on its own reliably - capillary action needs a continuous water column. Wet it through before you fit it.

2. Run it up into the root zone, not just into the soil. The top of the wick should sit in the middle third of the root ball. A wick that stops at the base of the pot wets the bottom inch and nothing else.

3. Keep the reservoir close. Capillary lift has a limit. Blumat publishes 12 inches as the maximum lift for its ceramic cones, and a cotton wick is working against the same physics. The further below the pot your water sits, the less arrives.

4. Leave the drainage hole working. A wick threaded through a drainage hole should not plug it. If the pot cannot drain when you top-water it, you cannot do the flush that a bottom-watered pot needs, and salts will build up on the surface.

How far below the pot can the water sit?

Capillary rise has a hard limit and it is the constraint people design around last. Blumat publishes 12 inches as the maximum lift for its ceramic cones - the reservoir has to sit no more than a foot below the cone or the vacuum cannot pull water up. A cotton wick is working against the same physics with less engineering behind it.

In practice that means the reservoir belongs immediately under the pot, not on the floor beside a plant stand. The common failure is a jar of water placed tidily at floor level with a long wick running up to a pot on a shelf: the wick is wet at the bottom, dry at the top, and the plant gets nothing while the jar stays full.

It also means height is the first thing to change when a setup underperforms. Raising the reservoir two inches costs nothing and does more than switching to a thicker cord.

What goes wrong, and how to read it

A wicking setup fails in one of four ways, and each has a distinct signature. This is worth knowing because the symptoms look identical from above the soil, which is the problem this whole site keeps running into.

Full reservoir, dry soil. The transport path has failed. Either the wick has mineralized stiff, it has lost contact with the mix, or the reservoir sits too low. This is the diagnostic that tells you the wick is the problem rather than the watering.

Empty reservoir, soggy soil. The wick is over-delivering for that pot - too thick, or too much of its length buried in the mix. Go thinner.

Soil wet at the bottom, dry at the top. The wick stops short. The top of it needs to sit in the middle third of the root ball, not at the base of the pot.

Pale crust on the surface, tips browning. Not a wick fault at all - that is salt accumulation from feeding a pot that never drains, and the fertilizer page covers the fix. A wick makes it more likely because water only ever travels upward.

Cotton or nylon

Cotton is what almost every wicking cord on the market is, and it works well. It is absorbent, cheap and flexible. It also rots, because it is an organic fiber held permanently wet, and in hard water it stiffens as calcium deposits accumulate in the fibers until it stops transporting.

Nylon does not rot and is slower to mineralize, which is why the one fitted-wick pot here uses it. The trade is absorbency: a synthetic fiber wicks by surface tension between filaments rather than by soaking, so it tends to be less forgiving about contact with the mix.

Nobody publishes a service life for either, so there is no number to settle this. The practical rule: if your water is hard, expect to replace a cotton wick and buy enough cord that doing so is trivial. If you do not know whether your water is hard, that is a cheap thing to measure and it affects more than your wicks.

Two thin wicks or one thick one?

This comes up because the honest answer to “what diameter?” is “try it and watch”, and people reasonably ask whether they can tune the rate without buying another spool.

You can, and two wicks is the more controllable of the two routes. Doubling the number of cords roughly doubles the cross-section carrying water, so two 1/6-inch cords land somewhere near one 1/4-inch cord - but you can remove one of them without replacing anything, which you cannot do with a single thicker cord. For a pot that is marginal in winter and thirsty in July, that is a genuinely useful adjustment.

The practical limit is contact area in the mix. Two cords entering at the same point do less than two cords spread to opposite sides of the root ball, because a wick only wets the mix it touches. Spread them, and keep both tops in the middle third of the root ball rather than coiled together at the base.

When a mat beats a wick

For a group of small pots, individually wicking each one is more work than the problem deserves. A felt capillary mat sits under a tray with its edge in water, and every pot standing on it draws through its own drainage holes. One component, no threading.

The limits are real. A pot with no drainage hole gets nothing. A single large plant draws more than a mat can move through its base. And permanently damp felt under a tray of pots is a fungus gnat habitat, which is a genuine cost rather than a theoretical one.

For vacation use specifically, a mat is usually the better of the two - our capillary mat page covers that case including how long one actually lasts. For a permanent setup on a windowsill, wicks give you per-pot control a shared mat cannot.

What we would buy

Converting pots you already own, mixed sizes: the five-diameter set. It costs less than a single planter, and finding out what your pots want beats guessing once.

You already know your diameter: the matching single spool. Fifty or sixty feet means you will never think about it again.

A tray of seedlings or small pots: the felt mat. Then read the seed tray page, because that is a solved problem with purpose-built kit.

You want it to just work: buy a planter with the wick fitted, or better, buy a reservoir planter that needs no wick at all and publishes its capacity. The indoor roundup covers those, and they are the ones whose refill interval we can actually compute.